Dermographism literally means “writing on the skin” [from Greek: dérma, dérmatos ‘skin’, gráphō ‘write’]. It is characterised by linear lesions appearing after linear pressure, for example scratching. Shape and location of the lesions are the projection of the stimulus. Red, urticarial and white dermographism can be distinguished.
• Red dermographism is a common erythemal reaction due to dilated blood vessels, it appears 15-20 seconds after skin rubbing.
• Urticarial dermographism is a type of physical urticaria. It appears most probably due to the release of histamine and other mediators from mast cells after mechanical stimulus, and resembles linear urticaria bumps.
• White dermographism is characterised by the presence of white stripes after skin rubbing. The presence of white dermographism is a small criterion of atopic dermatitis. It appears as a result of blood vessel contraction due to abnormal release of skin neuropeptides.